Add a performance testing tool

[adamncasey]

This PR adds a performance test tool useful for testing amqpprox performance.

An extract from the README.md included in the performance_tester directory:

amqpprox Performance Testing

amqpprox performance has been tested mainly in two ways:

1. Total data throughput achieved by connected clients (MB/s)
2. Total connection establishment throughput achieved (connections/s)

The performance tester in this folder helps with both of these by:

1. It contains a dummy AMQP 0.9.1. server which walks the AMQP handshake and ignores all future frames except close.
2. It can run parallel AMQP clients connecting to an amqpprox instance.
   1. Testing data throughput probably wants to send more, larger messages with fewer connections
   2. Testing connection throughput probably wants to send fewer, smaller messages with many connections.

Usage Help

amqpprox_perf_tester

USAGE:
    amqpprox_perf_tester [OPTIONS] --listen-address <LISTEN_ADDRESS>

OPTIONS:
        --address <ADDRESS>                  [default: amqp://localhost:5672/]
        --clients <CLIENTS>                  [default: 10]
    -h, --help                               Print help information
        --listen-address <LISTEN_ADDRESS>
        --listen-cert <LISTEN_CERT>
        --listen-key <LISTEN_KEY>
        --max-threads <MAX_THREADS>          [default: 50]
        --message-size <MESSAGE_SIZE>        [default: 100]
        --num-messages <NUM_MESSAGES>        [default: 10]

PR todo

• Fix any inevitable CI issues - off the top of my head the image we run the integration tests in will need to build rust code.

[adamncasey]

Squash & merge is disabled on this repo, possibly because of CLA concerns. I squashed locally